The present invention relates to a new and improved protective cutoff device for a gear wheel grinding machine.
In its more specific aspects the invention relates to a new and improved protective cutoff device for a gear wheel grinding machine which is of the type comprising a grinding wheel displaceable in a direction towards a tooth flank by means of a grinding wheel support or carrier, the position of which is automatically controlled, and further including a superimposed fluid operated, typically hydraulic automatic flank correction control containing a displacement measuring system operating a servo valve by means of a comparator for comparing set or reference values and actual values, the servo valve causing correction displacements of the grinding wheel support or carrier via an adjusting or adjustment cylinder operatively coupled thereto.
A gear wheel grinding machine of the type initially described and for which the protective cutoff device of the invention is intended is known, for example, from the journal "maschine+werkzeug", Coburg, Volume 23, 1979, pages 62-72. In this gear grinding machine the shape of the tooth flank is generated exclusively by kinematic movements. In most cases, however, the tooth flanks are not generated so as to form unchanged involute helical surfaces, rather must be provided with intended involute corrections and corrections of the tooth flank curve, so that the machine is equipped with a corresponding flank correction device. To achieve the desired flank corrections the axial position of the grinding wheel is continuously changed during the procedure and as a function of the generating and advancing or feed movements. The correction oscillations performed by the grinding wheel support or carrier therefor generally amount to some hundredths of a millimeter. The correction movements applied to the grinding wheel carrier originate from a computer. By means of the computer-controlled topologic flank correction device the tooth flank can be generated with a topography which can be freely selected within certain limits. Therefore, the computer processes the received data concerning the instantaneous generating and advance position and determines the feed or displacement value of the grinding wheel by comparison of a set or reference value and an actual value. This feed or displacement valve constitutes the flank correction adjustment for the corresponding coordinates of the tooth flank. For this purpose the computer-controlled topologic correction device includes a data input, a generating displacement pickup, feed or advance displacement pickup, the computer and the servo valve operated thereby. This servo valve acts upon the adjusting or adjustment cylinder in order to impart the correction movements to the grinding wheel carrier as measured by the actual value transmitter. The grinding wheel support or carrier is arranged upon a carriage or slide which is displaceable in correspondence to the desired flank profile or shape, and it is on this carriage that the movements corresponding to the desired flank correction are applied to the grinding wheel carrier by means of the adjusting cylinder.
In such a gear wheel grinding machine problems result in the event of a failure in the electric power or the pressure or when the power or pressure drops below a certain value. In that case the grinding wheel may remain in the position existing at the moment the failure arose and may undesirably grind a hole into the tooth flank during run-down of the grinding wheel to standstill. Alternatively, the grinding wheel support or carrier may assume an undefined position which will complicate the renewed start-up of the machine and the automatic position control of the grinding wheel support or carrier. When the grinding wheel support or carrier is mounted to a cross-beam or traverse and such is located in a position where the servo valve is loaded by a high pressure, then also the servo valve will assume an undefined position in the event of a pressure failure, for example, as a result of an electric power failure, which again has the consequence that the grinding wheel carrier assumes an undefined position.